大地電磁法探查台灣清水地熱區

MT study in Chingshui geothermal area of Taiwan

徐漢倫(Han-lun Hsu)

指導教授 ： 陳洲生

國立中央大學/地球科學學院/地球物理研究所/碩士(2007年)

摘要

宜蘭清水地區是台灣在1981年曾經發展過地熱發電的地區，但由於後期出水孔隙阻塞嚴重，熱水與蒸汽量的減少，導致清水地熱區發電終止運作。為了解深部是否有較佳的地熱潛能條件，本研究將使用能探測深部地層（大於1公里）的方法－大地電磁法(Magnetotellurics, MT)，對清水地區做的深部地層的調查。
MT使用上多有限制，特別易受人為電磁雜訊影響，本研究除了依循傳統的MT方法，並研究改善資料品質，包括延長資料收集時間、遠端參考站的使用以及GB張量分解等。
MT結果並參考前人研究與地質的分析，可以看出地熱區與低電阻構造呈現相關性，由此推估測區的地熱，極可能是來自清水地區南方深部8公里，但溫泉水的來源，應該只是天水深入地層受地熱加溫，再沿岩層裂隙出露地表，並非直接來自深層地熱水。测區有明顯熱源的集中，極具發電潛能，此外本研究還看到更深層的熱源在20公里以下，推測此深部的熱源可能來至台灣地區的板塊運動推擠有關，有待後續調查。

關鍵字

地熱 ； 大地電磁法 ； 電阻率

並列摘要

The Chingshui geothermal area in Yilan has ever been developed as a geothermal power plant in Taiwan, 1981. The power station was stopped operation because the water pipe had been blocked seriously and the hot water and steam reduced greatly. We did MT survey in order to understand whether there is potential geothermal energy in depth. For deep investigation, we used the magnetotelluric (MT) method that could analyze the deep structure more than 1 km.
To increase the signal to noise ratio, besides following the traditional MT data collection, we have tested to record MT data by prolonging time as long as three days and we also use the remote-reference for improving the quality of data. The result shows that three days record and remote-reference are needed for high quality MT data acquisition in Taiwan area. Then we use the Groom and Bailey decomposition analysis (GB decomposition) for the geoelectric strike determinations.
The result of MT study in Chingshui area shows the relation between geothermal source and low resistivity structure. We can suggest that the heat source comes from the south of the region and its depth is about 8 km. The hot spring could be the meteoric water which permeated into deep strata and was heated by geothermal source and then appeared on the earth’s surface along the fracture of strata. Thus, the Chingshui geothermal area is high potential for power plant. Lastly, we also find a deeper heat source that down to the depth of 20 km which is perhaps due to the collision of plates in Taiwan area.

並列關鍵字

Magnetotelluric(MT) ； geothermal ； resistivity

參考文獻

季松青，大地電磁資料多站多頻分析於台灣中部及金門地區地殼電性構造，國立中央大學博士論文，145頁，2006。

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Chang, Chung-Pai, Strain and stress field in Taiwan oblique convergent system: constraints from GPS observation and tectonic data, Earth and Planetary Science Letters, 214, 115-217, 2003.

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